Pseudohybrid microwave filter



W. D. LEWIS EVAL PSEUDOHYBRID MICROWAVE FILTER Nov. l1, 1952 2 SHEETS- SHEET l Filed oct. 7,r 1949 n'. o. L Ews .WENTORSJ R. ,1J/Ence Nov. 11, 1952 w. D. I Ewls Erm.

PSEUDOHYBRID MICROWAVE FILTER 2 SHEETS-SHEET 2 Filed Oct; 7, 1949 m D. L Ew/s 4 J. R. P/ERCE v ...Si

INVENTORS:

ATTORNEY Patented Nov. 11, 1952 PSEUDOHYBRID MCROWAVE FILTER Willard l). Lewis, Little Silver, and .lohn R. Pierce, Millburn, N. J., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a

corporation of New York Application October 7, 1949, Serial No. 120,141

(Cl. PTS- 44) This invention relates to improved microwave, wave filter structures. More particularly, it relates to microwave filters of the type in which frequency selective transmission between two microwave transmission lines is eiected by the combined action of a plurality of pairs of resonant structures interconnecting the transmission lines, at a like plurality of points spaced along the transmission lines, each pair of structures being coupled to each wave guide in a particular manner whereby each pair, together with the particular coupling arrangements, constitute a constant resistance filter, and the entire structure is therefore also of the constant resistance type.

For the purposes of this application the term microwave is to be understood to include frequencies from approximately 100 megacycles and higher.

The devices of the invention comprise various and sundry combinations of principles and of features of structures disclosed in applicant Lewis copending application Serial No. 120,142, iiled October 7, 1949, and those dis-closed in applicant Pierces copending application Serial No. 25,027, led May 4, 1948.

In other words, the present joint application is concerned with structures which comprise pluralities of Constant resistance pseudohybrid structures of types disclosed in the above-mentioned sole application of Lewis combined in accordance with principles disclosed and explained in the above-mentioned sole applications of Lewis fand Pierce, whereby unitary structures which have novel characteristics of a most useful nature are readily realized.

An object of the invention is therefore to provide novel forms of constant resistance microwave transducers. (The term transducer is to be understood to include wave filters and equalv izers.)

A further object of the invention is to proivide microwave transducers which combine the advantages of the paralleled resonator structures of the above-mentioned sole application of applicant Pierce with the pseudohybrid structures of the above-mentioned sole application of applicant Lewis.

A still further object of the invention is to provide microwave transducers which combine vthe advantages of the paralleled resonator structures of the above-mentioned sole application of applicant Pierce with the pseudohybrid constant resistance structures of theV above-mentoned sole application of applicant Lewis..

Other and additional objects will become apparent during the course of the following description of specic illustrative structures of the invention and fromthe appended claims.

The nature and principles of the invention will be more readily understood from the following detailed description of the several specific structures of the invention shown in the accompanying drawings in which:

Fig. l illustrates one way of providing a broad band transmission characteristic by the addition of the transmission characteristics of a plurality of relatively more narrow bandpass structures;

Fig. 2 shows a structure of the Vinvention, in which a plurality of one form of constant resistance pseudohybrid filters are arranged to constitute a constant resistance paralleled resonator type of i'llter structure;

Fig.l 3 is similar to Fig. .2 except that a plurality of a second form of pseudohybrid lters are employed; and

Fig. 4 is also similar to Fig. 2 except that a plurality of pairs' of constant resistance pseudohybrid lters are employed.

In more detail, in Fig. 1, four relatively narrow pass-bands centered about 3985, 3995, 4005 and 4015 megacycles, respectively, are superimposed and combined to provide a wide pass-band extending from 3985 to 4015 megacycles, inclusive. The four narrow pass-bands are those dened by the curved lines |00, |02; |04, |00; |03, ||0; and H2, H4, respectively. The broad passband, formed by the joint contributions of all four narrow bands, is that dened by the solid line ||6 and the lowermost and uppermost narrow band edges |00 and H4, respectively. The four narrow pass-bands can, by way of example, be those of units 1 to 4, inclusive, respectively, of Fig. 2, described in detail, immediately below.

In Fig. 2 a main wave guide 200 is, by way of example, a microwave transmission line carrying a plurality of frequency bands each of which bands constitutes a communication channel such as a television program channel.

It is desired to branch off one of these frequency bands, 'for example, the band extending between 3985 to 4015 megacycles, inclusive, and to direct the branched channel into a branch wave guide 202, 2|0; the other channels continuing undisturbed along wave guide 200. For this purpose four narrow band constant resistance pseudohybrid band-pass lter units, designated in Fig. 2 as units 2, 3 and ri, respectively, and having narrow pass-bands as illusdetail in that application. As shown for unit I.

in Fig. 2 of the accompanying drawings, each unit can comprise two resonators, orresonant cavities, 2 I0 220 electrically coupled loosely by apertures or irises 2 I2, 2 I6 and 2 I4, 2 I 8 to wave guides 200 and 202, respectively. In more detail, cavity 2I0 i-s coupled to the wider side of guide 200 by iris 2I2 and to the more narrow sideof guide 202 by iris 2M, whereas cavity 220 is 'connected to the more narrow side4 of guide 200 by iris 2l@ and to the wider sideof guide 202 by iris 2I8. The irises 2I2, 2M, 2I5vand ZIBarejdisplaced to one side of the lateral center lineoftheir respective cavities 2I0 and4 220,.as shown, tol avoid an unwanted balance which might be` unwittingly achieved and would prevent the passageof energy through the cavity..v The optimum displacement is thatV which places the irisesone-quarter wavelength further from onesidewall than the other, though any displacement will preclude ythe establishment of a perfectV balance. Theh side walls irrthis` instance are to be regarded as those adjoining the smallerends of` the walll in` which the particular iris is situated.- Y

Unii',s 2, 3 and Igor 1*',ig. 2 areV substantially identical t0. unit I `except thattheir ,respective cavities 250, 252 240,1 2412 and,20,0,26-2are tuned to resonance nearthemid-frequencies 399,54005 and 4015 megaeyeles. respestive-ly,.0i their passbands. whlethese of; unit .l .are tunedto res.- onance near the mid-frequency,39,85`A megacycles i. its pass-bami assuming, forexample. that units I to ofgliig. 2 lhave thenfour pass-,bands as shown from left torightninFig. 1 respectively. l

The branchguide 202 lZyllhas insertednear its Center point, an, additional half- Wavelength cem.- prlene. the we vertical; quarter.. wavelength legs 204Hand208, The lower endsof these are joined by tlee. heriientelpertien 2.0.6.1 This arrangement provides e. phase. shirt ef. Substantially .180. deerees leelweeihe .Cemeelleets Oferlerav, reaching the. -bfeneheuifie threueh .Units Ll .and Sandthe eempeneeie ,reeehies ,the .branch guide. through units 2 andi.U This isv desirable since, asis well known tovthoseF skilledj in the art, there is an inherent phase shift 0111801- degreesbetweenthe lower and` higher endsv of a frequency band `when transmitted through aAband-passlter. By adding 180 degrees to the lters of alternatel pass,

bands in'an aringelilent as describedinconnection with Fig, 2nV (the transmission A`characteristics of whicharewillustrated in Fig., 1) the frequencies of the upper end sof the pass-bands. of units I and 3, for` eXample, are ,broughtl into phase with the frequencies at ,the lower .ends of. the pass-bands of units 2.and 4, respectively. If this is not done the uniformity of transmission throughoutthe entirev composite band, i. ejrom 3985 to 4015 megacycles of Fig. 1, for example, will be destroyed oversmall frequency intervals about the pointswhere adjacent bands cross over orintersecteach other, i. e., about the points at which curves, I02, and |04; I0.6 and I08; and .IIB and II2, intersect. In some instances these" disturbances (narrow attenuation intervals) at cross-over lpoints may not be objectionable, particularly if no essential signal elements are present in these narrow frequency intervals, in which instances it is not necessary to provide for the additional lSO-degree phase shift of alternate channels. The equivalent of the above-described phase shift can, alternatively, be introduced by an appropriate selection of coupling means between the cavities and the branch guide as is disclosed vand described in detail in connection with several specic coupling arrangements shown in the drawings accompanying applicant Pierces above-mentioned copending application. (See also the coupling arrangement employed in Fig. 3 described below.)

Assuming that all channels or the system are introduced into the left end of guide 200, the selected .or branched channel will appear at the right end 203 of guide'202 and the other channelswill be transmitted to` theright endof the main guide 200. The left vendor` guide 202 is preferably terminated'iny its characteristic impedance at a distance of an odd number of quarter wavelengths or the median lfrequency of the band of frequencies to be branchedoft to guide 202, fromntlie coupling point oiA the `nearest unit (unit I). Asis well known tothose-.skilled inthe-art, the characteristic impedance of a wave-guide transmission line is sultlstantiallyaf'pure'V resistanceand a, wave guide canthe'reforelreadily be terminated in its' characteristic impedancebyinserting at the endvthereof afsuitableamount of resistance materialI such as carbonlparticles'or dielectric members coated With colloidalY carbon.

If the systemis perfectlyl balancedor if .minor impedance irregularities; efe .Het eblectefleblef. it can simply be short-circuited at one-quarter wavelength, or an odd number of quarterwavelengths, from the'lcouplingrpointofthe nearest unitA (unit I) Since'unitsj lto. 4;. incluhsiye, are eachconsta'nt resistance structures, per se, the yspacing `between coupling points of successive units canbe chosen purely from ihe standpoint.fefnmeeheeieelleenvenience in constructing and assembling thecomplete. Siruellre- Shellld. DrQbleHiS. Offllieleion and" impedance irregularities lee erleeeetered (they Should bevery smeltwater moet Purposes entirely negligible le, aearefellr designed-.ene constructed ever-ell. assemble); their een be fertlier-mieimiaed by ,Sneeineaihe eleee -lhe guides zee-ane 250.2, so, .that .meco-uniss remis 0f; Successive unit-e .alenaeeeh;if eide; ere-spaced en Odd number er 'ele-arieerweveleeethe@eert-lef the median frequency ors-the;bandfrotrrequencies t0 'be transmitted leguide-202% Alternatively, enr. 0i the .Several-ether diiereei .interv/altem SpangehoWn anddsrbei .mi n? Pplfaynt Pierces above-mentioned copending, application canbe employed. A d A' In Eig.` 3 an alternativelform. or .structure of the invention 'is shownwhich@diies-frorn that of Fi-g` 2 .principally finth'atfa' Ap1uralitylorconstant resistance pseudohybrid ,microwave wave filiere 0f the type SHOW? infie-,1776i applicant Lewis above-mentioned copending applicatiois employed to couple the main .and branch wave guides 30.0and;303-,Arespectively`lY` In .more detail eeel.1 efl-.these.eeeeeeliybridiltere ,(ve, ere Shewebrway. Qt example) eem- Prises twoJ resonators..whiehrorthe extremeleft unit .are designated Maand `3 0 l, Eachcrthese resonators is coupled to.b0ilh. waveguides. res: onator 3,04. ,being ,coupled to. main guide 300. .by member 334 which constitutes a coupling loop to the cavity and its free end is a probe into guide 300. The degree of coupling of guide 300 to the probe is determined by the extent to which tortion of the wave caused by protrusion of screw 330 into it. Cavity 304 is also coupled to guide 302 through an orifice 340 in the upper (broader) surface of the guide. Similarly, cavity 306 is coupled by element 338 and adjusting screw 332 to guide 302 and by orifice 336 to the lower (broader) side of guide 300.

Successive units along the guide from left to right comprise the pairs of resonators 308, 3|0; 352, 3|4; 3|6, 350; and 320, 322, respectively, and are coupled to the guides 300 and 302 as described above for the first unit at the extreme left. To provide a smooth over-all composite pass-band, as described in detail in connection with Fig. 2, in several of the units (for example in the second and fourth units) the loop portion of the probe can be turned through 180 degrees to provide the contrary coupling for them which was provided in Fig. 1 by insertion of the 18o-degree loop of Fig. 1 comprising portions of wave guide 264, 206, 200.

Each unit passes a relatively narrow band of i frequencies, vthe five units in conjunction passing a sufficiently broad band of frequencies to constitute a communication frequency channel suitable, for example, for a television channel.

Assuming that several broad band channels of a complex system are introduced into the left end of main guide 300, one will pass through the ve units and appear at the right end of guide 302, the others passing freely to the right end of main guide 306. The left end of guide 302 is preferably terminated in its characteristic impedance as described for guide 202 of Fig. 2. A1- ternative arrangements of the termination and center to center spacings of the coupling points for successive coupling units along the wave guides can also be as described for the over-all structure of Fig. 2.

In Fig. 4 a third alternative structure of the invention is shown which differs from those of Figs. 2 and 3 mainly in that a plurality of pseudohybrid microwave wave filters of the type shown in Fig. 19 of applicant Lewis above-mentioned copending application are used to couple the main guide 400 and the branch guide 402. The left end of guide 402 is preferably terminated in its characteristic impedance or it may be terminated in any of the alternative ways described above in connection with Fig. 2.

Each of the six pairs of connecting structures joining guides 400 and 402 can comprise a pair of pseudohybrid band-pass lters substantially as shown in detail for the pair at the left end of the gure. Of this pair the upper pseudohybrid band-pass filter comprises vertical arm 404, horizontal arm 4|4 and two lateral arms comprising resonant cavities 406, 400 coupled by irises 4|0, 4|2, respectively, to the throat section of the pseudohybrid junction as disclosed and described in detail in applicant Lewis abovementioned copending application.

Similarly, the lower pseudohybrid band-pass lter comprises vertical arm 420, horizontal arm 430 and resonant cavity, lateral arms 426, 428 coupled by irises 422, 424, respectively, to the throat section of the pseudohybrid junction The two pseudohybrid band-pass filters just described connect through irises 432 and 434 to guide 400 and through irses 4 l 6 and 418 to guide 402 forming two pseudohybrid junctions as shown and described in applicant Lewis above-mentioned copending application. The other pairs of connecting structures, namely, 436, 438; 440, 4.42; 444, 446; 448, 450; and 454, 456 are of the same kind as the extreme left pair described in detail above but are designed to pass five other narrow frequency bands, the six bands taken together providing for branching off to guide 402 a channel of frequencies of suitable width for some specific use such as a televisionchannel. Centerto-center intervals between the coupling points of successive lter pairs and the left end of guide 402 to nearest pair coupling point spacing, can be the same as for the structures of Figs. 2 and 3 as described above. In this instance the additional 18o-degree phase shift for alternate pairs of coupling filters can be obtained by inserting a one-quarter wavelength of wave guide between the iris and the throat section of the pseudohybrid junction of the two filters of the pair as indicated for lters 436, 438; 444, 446 and 454, 456. Specically in these cases a onequarter wavelength of wave guide 431 is added between each lateral cavity and the throat section of its associated filter, as shown in Fig. 4. Alternatively,the three units just described can be grouped at the right, the extra quarter wavelengths of wave guide 431 can be omitted, and an extra half wave loop can be added in either guide 400 or guide 402 (preferably 402 since it carries only energy of the channel to be branched off) between the groups precisely as was done in Fig. 2. A further alternative is, of course, toemploy appropriate coupling means such as the loop and probe coupling of Fig. 3 and reverse the phase of the coupling of those units for which a -degree phase shift is desired.

Numerous and varied additional arrangements in accordance with the principles and within the scope of the invention can, obviously, readily be devised by those skilled in the art. The abovedescribed embodiments are merely illustrative. By way of example, coaxial structure can be substituted for part or al1 of the wave-guide structure of the above embodiments without departing from the spirit and scope of the invention.

What is claimed is:

1. A microwave electromagnetic wave transducer comprising a plurality of pairs of electromagnetic wave resonating structures interconnected between two electromagnetic wave wave guides, one resonating structure of each pair being loosely coupled in parallel relation with a rst of said wave guides and loosely coupled in series relation with the second of said wave guides, the other resonating structure of said pair being loosely coupled in series relation with the first wave guide and loosely coupled in parallel relation with the second wave guide, the two coupling points of each pair to each wave guide being centered in a common plane perpendicular to the longitudinal axis of the wave guide.

2. The transducer of claim 1, the two resonating structures of each pair comprising resonant cavities having the same resonance frequency, said resonance frequency being different from that of any of the other pairs of cavities of the said plurality of pairs.

3. The transducer of claim 1, the two resonating structures of each pair comprising substantially identical electromagnetic wave pseudohybrid microwave Wave guide band-pass wave filters,

thebands, passentI by;l thefwave lters or succes.- sive. pairs being. displaoedginfrequency with re speot to each other.`

4. The transducer of-V claim: 1, the. couplings between the resonant structures and.- the. wave guides4 being effectedk by irises.

5. The transducer of claim. 1, a portionofthe couplings between thev resonant structures. and the-Wave guides being effected byY loop and. probe couplingl devices.

6. The transducer ofcl'aim 1. in whichonewave guide includesk an additional, half wavelengthof the median frequency of the-range of frequencies to be transmitted*betweensaidltwo wave guides, as compared with the other waveguide,- said ad,- ditional half Wavelength being situated between the coupling points of twoportionsofisaid plurality. of` pairs, of resonating structures.

'7.y A high frequency,A electromagnetic wave, transducer comprising. aplurality ofpairs of. high frequency, electromagnetic wave, resonant structures coupled between twohigh frequency, elec.- tromagnetc wave, Wave guides of rectangular cross-section, one cross-sectional dimension of each wave guide being greater. than the other cross-sectional dimensionof the same ,wave guide, one of the resonant structures of eachpair being coupled to a side of smaller crossfsectional di.- menSiQn of one wave guide and a sidevof greater cross-sectionalv dimension of the secondl wave guide, the other resonant structurel of the same pair being coupled' to a, side. of greater crosssectional. dimension of` said one wave guide and aside Off smallery erossfsectional dimension of said' other guide, the two ponteoi' coupling to each guide of each pairbeingin aeommon crosssectional area perpendicular to thelongitudinal axisof the guide.

8; The arrangementof; claim 7' in which suc,- cessive coupling areas are acorrespondingiinteirvalsY along both said guides,

9. The arrangement of` claimY 7 in whichY one en@ f '011e -OfV Samva-ver` guidesis terminated and the coupling points of;l the nearest pair, of; said 8*v resonant structures tosaid one of said Wave guides arespaced an oddnurnber of. quarter wavelengths of themedian frequency of the range of frequencies to be transmitted betweensad two wave guides from said, terminated wave-guide end.

10. In a microwave electromagneticwave waveguide transducer a. plurality` of pair of electromagneticy wave resenating structurescoupled between two electromagnetic wave wave guidesfeach pair of resonators, havinga` common resonant frequency which diiers from the resonant frequency of each of the others of said pairs, the twocoupling points of.v each pair of resonators to each Wave guidebeingA displacedQO degrees from eachotherin a common plane perpendicular to the longitiidinal1axisk of the Wave guide theA planes ofr coupling of said` pairs. of resonators to said wave guides being spaced along both of said wave guides.

11. The structure of claim 10 in which the coupling points of successive pairsof resonating structures are spaced at intervals of an oddnumber ofy quarter wavelengths of the median frequency of theirequencyrange to be transmitted between said wave guides, With respect to the next adjacent pairs of resonating structures.

l2, The structure of claim l0n iny which the couplings of aportion of said plurality of resonatingpairs to one of said waveguides are in phase opposition with respect to the couplings of the remainder of said pairs tosaid. one of said wave guides..

rIhev following references are ofk record in the file of, this patent:

UNITED STATES PATENTS Name Date Korman July 1, 1947 NumberI 

